Vice President Joe Biden, accompanied by Attorney General Eric Holder, speaks about gun control during a meeting with sportsmen’s groups and members of the Cabinet last week.

WASHINGTON — While President Barack Obama pledged to crack down on access to what he called “weapons of war” in the aftermath of last month’s schoolhouse massacre, the White House has calculated that a ban on military-style assault weapons will be exceedingly difficult to pass through Congress and is focusing on other measures it deems more politically achievable.

As a task force led by Vice President Joe Biden readies recommendations on reducing gun violence for delivery to the president this week, White House officials say a new ban will be an element of whatever final package is proposed.

But given the entrenched opposition from gun rights groups and their advocates on Capitol Hill, the White House is trying to avoid making its passage the sole definition of success and is emphasizing other new gun rules that could conceivably win bipartisan support and reduce gun deaths.

During a day of White House meetings on the issue on Thursday, including one with the National Rifle Association, Biden focused publicly on universal background checks for gun purchases and the need for more federal research on gun violence.

In 15 minutes of public remarks, Biden made no mention of curbing the production and sale of assault weapons, even though he was a prime author of such a law that passed in 1994 and expired 10 years later. Both he and the president say they strongly support an assault weapons ban.

But Biden noted that his former colleagues in the Senate have long been “pretty universally opposed to any restrictions on gun ownership or what type of weapons can be purchased.” He said they now seem more open to limits on the purchase of high-capacity magazines.

A spokesman for Obama said later in the afternoon that the vice president’s remarks merely reflect a desire for a broad approach to gun violence.

‘’President Obama has been clear that Congress should reinstate the assault weapons ban and that avoiding this issue just because it’s been politically difficult in the past is not an option,” said Matt Lehrich, the spokesman.

“He’s also stressed that no single piece of legislation alone can solve this problem, which is why he has asked Vice President Biden to explore a wide array of proposals on topics ranging from gun laws to mental health to school safety.”

The calculation on the assault weapons ban underscores the complicated politics of guns on Capitol Hill despite public outrage after a gunman killed 26 people, including 20 children, at Sandy Hook Elementary School in Newtown, Conn., in December.

While the massacre prompted some pro-gun lawmakers to endorse limits on assault weapons, Republicans who control the House Judiciary Committee still oppose such limits.

A statement by the NRA after Thursday’s meeting underscored the political challenges. The group issued a blistering statement accusing the White House of having an “agenda to attack the Second Amendment,” and said it would go to the halls of Congress in its efforts to stop gun restrictions.

‘’We will now take our commitment and meaningful contributions to members of Congress of both parties who are interested in having an honest conversation about what works — and what does not,” the statement said.

The calibrated public focus by Biden also reflects a tension within the administration and Democratic circles, with some gun control advocates pressing for a robust effort on the assault weapon ban and others leery of being caught in a losing cause at the expense of other measures with more chances of success.

While Biden has included Attorney General Eric H. Holder Jr., Janet Napolitano, the homeland security secretary, and other Cabinet officials in his working group, officials said the process is being driven by the White House.

In addition to the ammunition limits and expanded background checks, Biden’s group is looking at ways of keeping guns out of the hands of the mentally ill and cracking down on sales that are already illegal. One possibility is a straw purchaser law with prison terms for those who buy guns for others.

Some officials would like mandatory minimum sentences for gun law violations, but the White House in general does not like such sentences. Biden’s group is also considering seeking additional money to enforce existing laws.

Biden’s comment this week about taking executive action was seized on by some opponents as evidence that the president wanted to unilaterally restrict gun sales. But officials said executive action refers to limited measures like directing more attention and resources to pursuing violations of existing gun laws and studying gun violence.

The ammunition limit has drawn attention from Democrats in Congress, both because they think it might be easier to pass and because it might have more impact than an assault weapon ban. To pass the last assault weapon ban through a Democratic Congress more amenable to gun control, Biden had to accept compromises that allowed many guns to be sold.

The White House effort is coming even as some governors are seeking state legislation that would limit the availability of guns and ammunition. In Denver, Gov. John W. Hickenlooper, a Democrat, called Thursday for universal background checks on all gun sales in his state.

In New York, Gov. Andrew M. Cuomo has made gun control efforts a centerpiece of his next year in office, pledging to pass a tough new assault weapons ban in his state, limits on large-capacity magazines and measures to keep guns out of the hands of criminals and the mentally ill.

Obama’s push for new federal action is the first serious one in many years. Biden held several meetings with representatives of hunting and wildlife groups, advocates of gun ownership, and officials with the entertainment industry. At the start of the meetings Thursday, Biden said he would give Obama his recommendations on Tuesday, though they may not be made public until later.

In their own closed-door meetings with the vice president on Wednesday, gun control advocates emphasized their belief that measures other than the assault weapons ban could be even more effective in preventing the kinds of recent massacres that have captured public and political attention, several participants said.

‘’There’s a natural gravity that happens toward the ban in the wake of tragedies,” said Dan Gross, the president of the Brady Campaign to Prevent Gun Violence, who attended the meeting. “But it’s very important to point out that background checks could have an even bigger impact.”